fix for event lag

* moves glfwPollEvents to top of App loop, and sleep logic to after display update, so that UI events can be processed immediately
Merge pull request #3226 from tgfrerer/test-pollevents-snappyness

possible fix for event lag
ofGstUtils: fix crash on unref of sample caps
Merge branch 'master' of github.com:openframeworks/openFrameworks
ofGst: fixes for gstreamer 0.10
ofGstUtils: remove debug trace
fixes rPI install_dependencies. Closes #3212
Merge remote-tracking branch 'upstream/master'